text: from itertools import cycle
  import random
  import sys
  import pygame
  from pygame.locals import *
  
  FPS = 30
  SCREENWIDTH  = 288
  SCREENHEIGHT = 512
  PIPEGAPSIZE  = 100 # gap between upper and lower part of pipe
  BASEY        = SCREENHEIGHT * 0.79
  # image, sound and hitmask  dicts
  IMAGES, SOUNDS, HITMASKS = {}, {}, {}
  
  # list of all possible players (tuple of 3 positions of flap)
  PLAYERS_LIST = (
      # red bird
      (
          'assets/sprites/redbird-upflap.png',
          'assets/sprites/redbird-midflap.png',
          'assets/sprites/redbird-downflap.png',
      ),
      # blue bird
      (
          'assets/sprites/bluebird-upflap.png',
          'assets/sprites/bluebird-midflap.png',
          'assets/sprites/bluebird-downflap.png',
      ),
      # yellow bird
      (
          'assets/sprites/yellowbird-upflap.png',
          'assets/sprites/yellowbird-midflap.png',
          'assets/sprites/yellowbird-downflap.png',
      ),
  )
  
  # list of backgrounds
  BACKGROUNDS_LIST = (
      'assets/sprites/background-day.png',
      'assets/sprites/background-night.png',
  )
  
  # list of pipes
  PIPES_LIST = (
      'assets/sprites/pipe-green.png',
      'assets/sprites/pipe-red.png',
  )
  
  
  try:
      xrange
  except NameError:
      xrange = range
  
  
  def main():
      global SCREEN, FPSCLOCK
      pygame.init()
      FPSCLOCK = pygame.time.Clock()
      SCREEN = pygame.display.set_mode((SCREENWIDTH, SCREENHEIGHT))
      pygame.display.set_caption('Flappy Bird')
  
      # numbers sprites for score display
      IMAGES['numbers'] = (
          pygame.image.load('assets/sprites/0.png').convert_alpha(),
          pygame.image.load('assets/sprites/1.png').convert_alpha(),
          pygame.image.load('assets/sprites/2.png').convert_alpha(),
          pygame.image.load('assets/sprites/3.png').convert_alpha(),
          pygame.image.load('assets/sprites/4.png').convert_alpha(),
          pygame.image.load('assets/sprites/5.png').convert_alpha(),
          pygame.image.load('assets/sprites/6.png').convert_alpha(),
          pygame.image.load('assets/sprites/7.png').convert_alpha(),
          pygame.image.load('assets/sprites/8.png').convert_alpha(),
          pygame.image.load('assets/sprites/9.png').convert_alpha()
      )
  
      # game over sprite
      IMAGES['gameover'] = pygame.image.load('assets/sprites/gameover.png').convert_alpha()
      # message sprite for welcome screen
      IMAGES['message'] = pygame.image.load('assets/sprites/message.png').convert_alpha()
      # base (ground) sprite
      IMAGES['base'] = pygame.image.load('assets/sprites/base.png').convert_alpha()
  
      # sounds
      if 'win' in sys.platform:
          soundExt = '.wav'
      else:
          soundExt = '.ogg'
  
      SOUNDS['die']    = pygame.mixer.Sound('assets/audio/die' + soundExt)
      SOUNDS['hit']    = pygame.mixer.Sound('assets/audio/hit' + soundExt)
      SOUNDS['point']  = pygame.mixer.Sound('assets/audio/point' + soundExt)
      SOUNDS['swoosh'] = pygame.mixer.Sound('assets/audio/swoosh' + soundExt)
      SOUNDS['wing']   = pygame.mixer.Sound('assets/audio/wing' + soundExt)
  
      while True:
          # select random background sprites
          randBg = random.randint(0, len(BACKGROUNDS_LIST) - 1)
          IMAGES['background'] = pygame.image.load(BACKGROUNDS_LIST[randBg]).convert()
  
          # select random player sprites
          randPlayer = random.randint(0, len(PLAYERS_LIST) - 1)
          IMAGES['player'] = (
              pygame.image.load(PLAYERS_LIST[randPlayer][0]).convert_alpha(),
              pygame.image.load(PLAYERS_LIST[randPlayer][1]).convert_alpha(),
              pygame.image.load(PLAYERS_LIST[randPlayer][2]).convert_alpha(),
          )
  
          # select random pipe sprites
          pipeindex = random.randint(0, len(PIPES_LIST) - 1)
          IMAGES['pipe'] = (
              pygame.transform.flip(
                  pygame.image.load(PIPES_LIST[pipeindex]).convert_alpha(), False, True),
              pygame.image.load(PIPES_LIST[pipeindex]).convert_alpha(),
          )
  
          # hitmask for pipes
          HITMASKS['pipe'] = (
              getHitmask(IMAGES['pipe'][0]),
              getHitmask(IMAGES['pipe'][1]),
          )
  
          # hitmask for player
          HITMASKS['player'] = (
              getHitmask(IMAGES['player'][0]),
              getHitmask(IMAGES['player'][1]),
              getHitmask(IMAGES['player'][2]),
          )
  
          movementInfo = showWelcomeAnimation()
          crashInfo = mainGame(movementInfo)
          showGameOverScreen(crashInfo)
  
  
  def showWelcomeAnimation():
      """Shows welcome screen animation of flappy bird"""
      # index of player to blit on screen
      playerIndex = 0
      playerIndexGen = cycle([0, 1, 2, 1])
      # iterator used to change playerIndex after every 5th iteration
      loopIter = 0
  
      playerx = int(SCREENWIDTH * 0.2)
      playery = int((SCREENHEIGHT - IMAGES['player'][0].get_height()) / 2)
  
      messagex = int((SCREENWIDTH - IMAGES['message'].get_width()) / 2)
      messagey = int(SCREENHEIGHT * 0.12)
  
      basex = 0
      # amount by which base can maximum shift to left
      baseShift = IMAGES['base'].get_width() - IMAGES['background'].get_width()
  
      # player shm for up-down motion on welcome screen
      playerShmVals = {'val': 0, 'dir': 1}
  
      while True:
          for event in pygame.event.get():
              if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
                  pygame.quit()
                  sys.exit()
              if event.type == KEYDOWN and (event.key == K_SPACE or event.key == K_UP):
                  # make first flap sound and return values for mainGame
                  SOUNDS['wing'].play()
                  return {
                      'playery': playery + playerShmVals['val'],
                      'basex': basex,
                      'playerIndexGen': playerIndexGen,
                  }
  
          # adjust playery, playerIndex, basex
          if (loopIter + 1) % 5 == 0:
              playerIndex = next(playerIndexGen)
          loopIter = (loopIter + 1) % 30
          basex = -((-basex + 4) % baseShift)
          playerShm(playerShmVals)
  
          # draw sprites
          SCREEN.blit(IMAGES['background'], (0,0))
          SCREEN.blit(IMAGES['player'][playerIndex],
                      (playerx, playery + playerShmVals['val']))
          SCREEN.blit(IMAGES['message'], (messagex, messagey))
          SCREEN.blit(IMAGES['base'], (basex, BASEY))
  
          pygame.display.update()
          FPSCLOCK.tick(FPS)
  
  
  def mainGame(movementInfo):
      score = playerIndex = loopIter = 0
      playerIndexGen = movementInfo['playerIndexGen']
      playerx, playery = int(SCREENWIDTH * 0.2), movementInfo['playery']
  
      basex = movementInfo['basex']
      baseShift = IMAGES['base'].get_width() - IMAGES['background'].get_width()
  
      # get 2 new pipes to add to upperPipes lowerPipes list
      newPipe1 = getRandomPipe()
      newPipe2 = getRandomPipe()
  
      # list of upper pipes
      upperPipes = [
          {'x': SCREENWIDTH + 200, 'y': newPipe1[0]['y']},
          {'x': SCREENWIDTH + 200 + (SCREENWIDTH / 2), 'y': newPipe2[0]['y']},
      ]
  
      # list of lowerpipe
      lowerPipes = [
          {'x': SCREENWIDTH + 200, 'y': newPipe1[1]['y']},
          {'x': SCREENWIDTH + 200 + (SCREENWIDTH / 2), 'y': newPipe2[1]['y']},
      ]
  
      dt = FPSCLOCK.tick(FPS)/1000
      pipeVelX = -128 * dt
  
      # player velocity, max velocity, downward acceleration, acceleration on flap
      playerVelY    =  -9   # player's velocity along Y, default same as playerFlapped
      playerMaxVelY =  10   # max vel along Y, max descend speed
      playerMinVelY =  -8   # min vel along Y, max ascend speed
      playerAccY    =   1   # players downward acceleration
      playerRot     =  45   # player's rotation
      playerVelRot  =   3   # angular speed
      playerRotThr  =  20   # rotation threshold
      playerFlapAcc =  -9   # players speed on flapping
      playerFlapped = False # True when player flaps
  
  
      while True:
          for event in pygame.event.get():
              if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
                  pygame.quit()
                  sys.exit()
              if event.type == KEYDOWN and (event.key == K_SPACE or event.key == K_UP):
                  if playery > -2 * IMAGES['player'][0].get_height():
                      playerVelY = playerFlapAcc
                      playerFlapped = True
                      SOUNDS['wing'].play()
  
          # check for crash here
          crashTest = checkCrash({'x': playerx, 'y': playery, 'index': playerIndex},
                                 upperPipes, lowerPipes)
          if crashTest[0]:
              return {
                  'y': playery,
                  'groundCrash': crashTest[1],
                  'basex': basex,
                  'upperPipes': upperPipes,
                  'lowerPipes': lowerPipes,
                  'score': score,
                  'playerVelY': playerVelY,
                  'playerRot': playerRot
              }
  
          # check for score
          playerMidPos = playerx + IMAGES['player'][0].get_width() / 2
          for pipe in upperPipes:
              pipeMidPos = pipe['x'] + IMAGES['pipe'][0].get_width() / 2
              if pipeMidPos <= playerMidPos < pipeMidPos + 4:
                  score += 1
                  SOUNDS['point'].play()
  
          # playerIndex basex change
          if (loopIter + 1) % 3 == 0:
              playerIndex = next(playerIndexGen)
          loopIter = (loopIter + 1) % 30
          basex = -((-basex + 100) % baseShift)
  
          # rotate the player
          if playerRot > -90:
              playerRot -= playerVelRot
  
          # player's movement
          if playerVelY < playerMaxVelY and not playerFlapped:
              playerVelY += playerAccY
          if playerFlapped:
              playerFlapped = False
  
              # more rotation to cover the threshold (calculated in visible rotation)
              playerRot = 45
  
          playerHeight = IMAGES['player'][playerIndex].get_height()
          playery += min(playerVelY, BASEY - playery - playerHeight)
  
          # move pipes to left
          for uPipe, lPipe in zip(upperPipes, lowerPipes):
              uPipe['x'] += pipeVelX
              lPipe['x'] += pipeVelX
  
          # add new pipe when first pipe is about to touch left of screen
          if 3 > len(upperPipes) > 0 and 0 < upperPipes[0]['x'] < 5:
              newPipe = getRandomPipe()
              upperPipes.append(newPipe[0])
              lowerPipes.append(newPipe[1])
  
          # remove first pipe if its out of the screen
          if len(upperPipes) > 0 and upperPipes[0]['x'] < -IMAGES['pipe'][0].get_width():
              upperPipes.pop(0)
              lowerPipes.pop(0)
  
          # draw sprites
          SCREEN.blit(IMAGES['background'], (0,0))
  
          for uPipe, lPipe in zip(upperPipes, lowerPipes):
              SCREEN.blit(IMAGES['pipe'][0], (uPipe['x'], uPipe['y']))
              SCREEN.blit(IMAGES['pipe'][1], (lPipe['x'], lPipe['y']))
  
          SCREEN.blit(IMAGES['base'], (basex, BASEY))
          # print score so player overlaps the score
          showScore(score)
  
          # Player rotation has a threshold
          visibleRot = playerRotThr
          if playerRot <= playerRotThr:
              visibleRot = playerRot
          
          playerSurface = pygame.transform.rotate(IMAGES['player'][playerIndex], visibleRot)
          SCREEN.blit(playerSurface, (playerx, playery))
  
          pygame.display.update()
          FPSCLOCK.tick(FPS)
  
  
  def showGameOverScreen(crashInfo):
      """crashes the player down and shows gameover image"""
      score = crashInfo['score']
      playerx = SCREENWIDTH * 0.2
      playery = crashInfo['y']
      playerHeight = IMAGES['player'][0].get_height()
      playerVelY = crashInfo['playerVelY']
      playerAccY = 2
      playerRot = crashInfo['playerRot']
      playerVelRot = 7
  
      basex = crashInfo['basex']
  
      upperPipes, lowerPipes = crashInfo['upperPipes'], crashInfo['lowerPipes']
  
      # play hit and die sounds
      SOUNDS['hit'].play()
      if not crashInfo['groundCrash']:
          SOUNDS['die'].play()
  
      while True:
          for event in pygame.event.get():
              if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
                  pygame.quit()
                  sys.exit()
              if event.type == KEYDOWN and (event.key == K_SPACE or event.key == K_UP):
                  if playery + playerHeight >= BASEY - 1:
                      return
  
          # player y shift
          if playery + playerHeight < BASEY - 1:
              playery += min(playerVelY, BASEY - playery - playerHeight)
  
          # player velocity change
          if playerVelY < 15:
              playerVelY += playerAccY
  
          # rotate only when it's a pipe crash
          if not crashInfo['groundCrash']:
              if playerRot > -90:
                  playerRot -= playerVelRot
  
          # draw sprites
          SCREEN.blit(IMAGES['background'], (0,0))
  
          for uPipe, lPipe in zip(upperPipes, lowerPipes):
              SCREEN.blit(IMAGES['pipe'][0], (uPipe['x'], uPipe['y']))
              SCREEN.blit(IMAGES['pipe'][1], (lPipe['x'], lPipe['y']))
  
          SCREEN.blit(IMAGES['base'], (basex, BASEY))
          showScore(score)
  
          
  
  
          playerSurface = pygame.transform.rotate(IMAGES['player'][1], playerRot)
          SCREEN.blit(playerSurface, (playerx,playery))
          SCREEN.blit(IMAGES['gameover'], (50, 180))
  
          FPSCLOCK.tick(FPS)
          pygame.display.update()
  
  
  def playerShm(playerShm):
      """oscillates the value of playerShm['val'] between 8 and -8"""
      if abs(playerShm['val']) == 8:
          playerShm['dir'] *= -1
  
      if playerShm['dir'] == 1:
           playerShm['val'] += 1
      else:
          playerShm['val'] -= 1
  
  
  def getRandomPipe():
      """returns a randomly generated pipe"""
      # y of gap between upper and lower pipe
      gapY = random.randrange(0, int(BASEY * 0.6 - PIPEGAPSIZE))
      gapY += int(BASEY * 0.2)
      pipeHeight = IMAGES['pipe'][0].get_height()
      pipeX = SCREENWIDTH + 10
  
      return [
          {'x': pipeX, 'y': gapY - pipeHeight},  # upper pipe
          {'x': pipeX, 'y': gapY + PIPEGAPSIZE}, # lower pipe
      ]
  
  
  def showScore(score):
      """displays score in center of screen"""
      scoreDigits = [int(x) for x in list(str(score))]
      totalWidth = 0 # total width of all numbers to be printed
  
      for digit in scoreDigits:
          totalWidth += IMAGES['numbers'][digit].get_width()
  
      Xoffset = (SCREENWIDTH - totalWidth) / 2
  
      for digit in scoreDigits:
          SCREEN.blit(IMAGES['numbers'][digit], (Xoffset, SCREENHEIGHT * 0.1))
          Xoffset += IMAGES['numbers'][digit].get_width()
  
  
  def checkCrash(player, upperPipes, lowerPipes):
      """returns True if player collides with base or pipes."""
      pi = player['index']
      player['w'] = IMAGES['player'][0].get_width()
      player['h'] = IMAGES['player'][0].get_height()
  
      # if player crashes into ground
      if player['y'] + player['h'] >= BASEY - 1:
          return [True, True]
      else:
  
          playerRect = pygame.Rect(player['x'], player['y'],
                        player['w'], player['h'])
          pipeW = IMAGES['pipe'][0].get_width()
          pipeH = IMAGES['pipe'][0].get_height()
  
          for uPipe, lPipe in zip(upperPipes, lowerPipes):
              # upper and lower pipe rects
              uPipeRect = pygame.Rect(uPipe['x'], uPipe['y'], pipeW, pipeH)
              lPipeRect = pygame.Rect(lPipe['x'], lPipe['y'], pipeW, pipeH)
  
              # player and upper/lower pipe hitmasks
              pHitMask = HITMASKS['player'][pi]
              uHitmask = HITMASKS['pipe'][0]
              lHitmask = HITMASKS['pipe'][1]
  
              # if bird collided with upipe or lpipe
              uCollide = pixelCollision(playerRect, uPipeRect, pHitMask, uHitmask)
              lCollide = pixelCollision(playerRect, lPipeRect, pHitMask, lHitmask)
  
              if uCollide or lCollide:
                  return [True, False]
  
      return [False, False]
  
  def pixelCollision(rect1, rect2, hitmask1, hitmask2):
      """Checks if two objects collide and not just their rects"""
      rect = rect1.clip(rect2)
  
      if rect.width == 0 or rect.height == 0:
          return False
  
      x1, y1 = rect.x - rect1.x, rect.y - rect1.y
      x2, y2 = rect.x - rect2.x, rect.y - rect2.y
  
      for x in xrange(rect.width):
          for y in xrange(rect.height):
              if hitmask1[x1+x][y1+y] and hitmask2[x2+x][y2+y]:
                  return True
      return False
  
  def getHitmask(image):
      """returns a hitmask using an image's alpha."""
      mask = []
      for x in xrange(image.get_width()):
          mask.append([])
          for y in xrange(image.get_height()):
              mask[x].append(bool(image.get_at((x,y))[3]))
      return mask
  
  if __name__ == '__main__':
      main()
  